This invention relates to negative resistance elements. Such elements can be considered as being of two types: voltage-controlled and current-controlled. A voltage-controlled negative resistance element is defined herein as an electical device having the property that an increase in the voltage applied across it will result in a decrease in the current flowing through it in the direction of the applied voltage (or an increase in the current flowing through it in the direction opposite to that of the applied voltage). Similarly, a current-controlled negative resistance element is defined herein as an electrical device having the property that an increase in the current flowing through it will result in a decrease in the voltage drop across it in the direction of the current flow.
The object of the present invention is to provide a novel form of voltage-controlled negative resistance element. The invention makes use of a circuit arrangement known as a current mirror. A current mirror basically comprises two matched transistors with their bases and emitters interconnected so that the current through one of the transistors is accurately reproduced in the other. Such an arrangement is described for example in British Pat. No. 1410021.